scholarly journals Recruitment of functionally distinct membrane proteins to chromatin mediates nuclear envelope formation in vivo

2009 ◽  
Vol 186 (6) ◽  
pp. 929-929
Author(s):  
Daniel J. Anderson ◽  
Jesse D. Vargas ◽  
Joshua P. Hsiao ◽  
Martin W. Hetzer
Keyword(s):  
Membrane Proteins ◽  
Nuclear Envelope ◽  
Nuclear Envelope Formation ◽  
Distinct Membrane

scholarly journals Recruitment of functionally distinct membrane proteins to chromatin mediates nuclear envelope formation in vivo

2009 ◽  
Vol 186 (2) ◽  
pp. 183-191 ◽  
Author(s):  
Daniel J. Anderson ◽  
Jesse D. Vargas ◽  
Joshua P. Hsiao ◽  
Martin W. Hetzer
Keyword(s):  
Membrane Proteins ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Time Frame ◽  
Lamin B Receptor ◽  
Chromosome Separation ◽  
Nuclear Envelope Formation ◽  
Membrane Components ◽  
Redundant Functions

Formation of the nuclear envelope (NE) around segregated chromosomes occurs by the reshaping of the endoplasmic reticulum (ER), a reservoir for disassembled nuclear membrane components during mitosis. In this study, we show that inner nuclear membrane proteins such as lamin B receptor (LBR), MAN1, Lap2β, and the trans-membrane nucleoporins Ndc1 and POM121 drive the spreading of ER membranes into the emerging NE via their capacity to bind chromatin in a collaborative manner. Despite their redundant functions, decreasing the levels of any of these trans-membrane proteins by RNAi-mediated knockdown delayed NE formation, whereas increasing the levels of any of them had the opposite effect. Furthermore, acceleration of NE formation interferes with chromosome separation during mitosis, indicating that the time frame over which chromatin becomes membrane enclosed is physiologically relevant and regulated. These data suggest that functionally distinct classes of chromatin-interacting membrane proteins, which are present at nonsaturating levels, collaborate to rapidly reestablish the nuclear compartment at the end of mitosis.

scholarly journals Reshaping of the endoplasmic reticulum limits the rate for nuclear envelope formation

2008 ◽  
Vol 182 (5) ◽  
pp. 911-924 ◽  
Author(s):  
Daniel J. Anderson ◽  
Martin W. Hetzer
Keyword(s):  
Endoplasmic Reticulum ◽  
Nuclear Envelope ◽  
Mammalian Cells ◽  
Time Lapse ◽  
Principal Mechanism ◽  
Nuclear Assembly ◽  
Nuclear Envelope Formation ◽  
Rate Limiting

During mitosis in metazoans, segregated chromosomes become enclosed by the nuclear envelope (NE), a double membrane that is continuous with the endoplasmic reticulum (ER). Recent in vitro data suggest that NE formation occurs by chromatin-mediated reorganization of the tubular ER; however, the basic principles of such a membrane-reshaping process remain uncharacterized. Here, we present a quantitative analysis of nuclear membrane assembly in mammalian cells using time-lapse microscopy. From the initial recruitment of ER tubules to chromatin, the formation of a membrane-enclosed, transport-competent nucleus occurs within ∼12 min. Overexpression of the ER tubule-forming proteins reticulon 3, reticulon 4, and DP1 inhibits NE formation and nuclear expansion, whereas their knockdown accelerates nuclear assembly. This suggests that the transition from membrane tubules to sheets is rate-limiting for nuclear assembly. Our results provide evidence that ER-shaping proteins are directly involved in the reconstruction of the nuclear compartment and that morphological restructuring of the ER is the principal mechanism of NE formation in vivo.

scholarly journals Lamins in disease: why do ubiquitously expressed nuclear envelope proteins give rise to tissue-specific disease phenotypes?

2001 ◽  
Vol 114 (1) ◽  
pp. 9-19 ◽  
Author(s):  
C.J. Hutchison ◽  
M. Alvarez-Reyes ◽  
O.A. Vaughan
Keyword(s):  
Membrane Proteins ◽  
Nuclear Envelope ◽  
Dna Sequences ◽  
Genetic Disorders ◽  
Integral Membrane Proteins ◽  
Partial Lipodystrophy ◽  
Nuclear Lamins ◽  
Disease Phenotypes

The nuclear lamina is a filamentous structure composed of lamins that supports the inner nuclear membrane. Several integral membrane proteins including emerin, LBR, LAP1 and LAP2 bind to nuclear lamins in vitro and can influence lamin function and dynamics in vivo. Results from various studies suggest that lamins function in DNA replication and nuclear envelope assembly and determine the size and shape of the nuclear envelope. In addition, lamins also bind chromatin and certain DNA sequences, and might influence chromosome position. Recent evidence has revealed that mutations in A-type lamins give rise to a range of rare, but dominant, genetic disorders, including Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy with conduction-system disease and Dunnigan-type familial partial lipodystrophy. An examination of how lamins A/C, emerin and other integral membrane proteins interact at the INM provides the basis for a novel model for how mutations that promote disease phenotypes are likely to influence these interactions and therefore cause cellular pathology through a combination of weakness of the lamina or altered gene expression.

scholarly journals Coordinated binding of Vps4 to ESCRT-III drives membrane neck constriction during MVB vesicle formation

2014 ◽  
Vol 205 (1) ◽  
pp. 33-49 ◽  
Author(s):  
Manuel Alonso Y Adell ◽  
Georg F. Vogel ◽  
Mehrshad Pakdel ◽  
Martin Müller ◽  
Herbert Lindner ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Adenosine Triphosphatase ◽  
Electron Tomography ◽  
Vesicle Formation ◽  
Multivesicular Bodies ◽  
Membrane Remodeling ◽  
Yeast Genetics ◽  
Endosomal Sorting ◽  
Distinct Membrane

Five endosomal sorting complexes required for transport (ESCRTs) mediate the degradation of ubiquitinated membrane proteins via multivesicular bodies (MVBs) in lysosomes. ESCRT-0, -I, and –II interact with cargo on endosomes. ESCRT-II also initiates the assembly of a ringlike ESCRT-III filament consisting of Vps20, Snf7, Vps24, and Vps2. The AAA–adenosine triphosphatase Vps4 disassembles and recycles the ESCRT-III complex, thereby terminating the ESCRT pathway. A mechanistic role for Vps4 in intraluminal vesicle (ILV) formation has been unclear. By combining yeast genetics, biochemistry, and electron tomography, we find that ESCRT-III assembly on endosomes is required to induce or stabilize the necks of growing MVB ILVs. Yet, ESCRT-III alone is not sufficient to complete ILV biogenesis. Rather, binding of Vps4 to ESCRT-III, coordinated by interactions with Vps2 and Snf7, is coupled to membrane neck constriction during ILV formation. Thus, Vps4 not only recycles ESCRT-III subunits but also cooperates with ESCRT-III to drive distinct membrane-remodeling steps, which lead to efficient membrane scission at the end of ILV biogenesis in vivo.

scholarly journals Role of the Endocytic Machinery in the Sorting of Lysosome-associated Membrane Proteins

2005 ◽  
Vol 16 (9) ◽  
pp. 4231-4242 ◽  
Author(s):  
Katy Janvier ◽  
Juan S. Bonifacino
Keyword(s):  
Plasma Membrane ◽  
Coat Protein ◽  
Membrane Proteins ◽  
Adaptor Protein ◽  
The Other ◽  
Sorting Signals ◽  
Efficient Delivery ◽  
Endocytic Machinery

The limiting membrane of the lysosome contains a group of transmembrane glycoproteins named lysosome-associated membrane proteins (Lamps). These proteins are targeted to lysosomes by virtue of tyrosine-based sorting signals in their cytosolic tails. Four adaptor protein (AP) complexes, AP-1, AP-2, AP-3, and AP-4, interact with such signals and are therefore candidates for mediating sorting of the Lamps to lysosomes. However, the role of these complexes and of the coat protein, clathrin, in sorting of the Lamps in vivo has either not been addressed or remains controversial. We have used RNA interference to show that AP-2 and clathrin—and to a lesser extent the other AP complexes—are required for efficient delivery of the Lamps to lysosomes. Because AP-2 is exclusively associated with plasma membrane clathrin coats, our observations imply that a significant population of Lamps traffic via the plasma membrane en route to lysosomes.

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